Effects of Melengestrol Acetate on L-selectin and β2-integrin Expression of Polymorphonuclear Leukocytes from Heifers Challenged with Lipopolysaccharide

Sixteen crossbred heifers were used in completely randomized design to determine the effects of melengestrol acetate (MGA) on polymorphonuclear leukocyte (PMN) L-selectin and β2-integrin expression and leukocyte numbers in heifers following Escherichia coli endotoxin (LPS) injection. On d 0, cattle were stratified by weight and randomly assigned, within strata, to diets they were fed throughout the trial. The diets consisted of 53.4% concentrate, 46.6% alfalfa hay, and either 0 or 0.5 mg MGA per heifer daily. On d 24, 1.0 μg/kg BW E. coli LPS was injected intravenously via jugular venipuncture. Blood samples were taken on d 0, 21, and 24 (4 h after LPS injection) and subjected to differential leukocyte counts as well as flow cytometric analysis of CD11b, CD11c CD18, CD62L, MHC1, and CD45 expression on PMN. Rectal temperatures were also recorded on d 24 (0 and 4 h after LPS injection). Following LPS injection, heifers in both treatment groups experienced decreases in circulating concentrations of all leukocyte populations (effect of sampling time P < 0.01), except eosinophils, which increased (effect of sampling time P < 0.06). Heifers fed MGA had higher overall circulating concentrations of neutrophils Effects of Melengestrol Acetate on L-selectin and β2-integrin Expression of Polymorphonuclear Leukocytes from Heifers Challenged with